Since an ethylenically unsaturated compound is prone to be extremely polymerized by heat, light and other factors, a solid is often generated by polymerization in the steps of producing and purifying an ethylenically unsaturated compound and causes the failure of production facilities. When the solid adheres to a production tank, a distillation column, a pipe and the like in the steps of producing and purifying an ethylenically unsaturated compound, not only, e.g., clogging due to the solid and anchoring of mobile facilities occur but also the solid interferes with the production and purification of the ethylenically unsaturated compound. In addition, the removal of the solid adhering to related facilities is generally performed by operation by human power and therefore has poor operation efficiency, a long-term shutdown is thus unavoidable, and an economic loss is large. Also, the deterioration of product quality is also caused.
Although it is known that the addition of various solid polymerization inhibitors is effective as a method for preventing the polymerization of an ethylenically unsaturated compound, only the addition is insufficient and many polymerization preventing methods other than the method have been proposed or performed.
For example, there has been proposed a method of adding a compound, in which Michael addition of alcohol or (meth)acrylic acid to a (meth)acrylic acid ester occurs, in a low-boiling point impurity distilling step of a crude (meth)acrylic acid ester (Patent Literature 1). However, this method is less effective since alcohol in a Michael addition moiety is desorbed by heating to reproduce a (meth)acrylic group in the case of using the Michael adduct of an alcohol or is ineffective from the viewpoint of the prevention of polymerization since there is still a (meth)acrylic group which is polymerizable in the case of using the compound in which the Michael addition of (meth)acrylic acid occurs. Furthermore, the addition of various impurities having such different strictures is not preferred since a functionally adverse effect is caused when using the product to make a secondary product (such as a resin molding, a coating or an optical material).
In view of the above, the advent of a method for more effectively preventing the polymerization of an ethylenically unsaturated compound has been earnestly desired.